Multiphase addressing method for transferring address information

ABSTRACT

A method of performing a burst read access at a memory device using a multiplexed data/address bus and a control signal including transferring a first portion of address information in a first phase via the multiplexed data/address bus to the memory device; transferring second portion of address information in a second phase via a multiplexed data/address bus to the memory device; transferring a series of data words from the memory via the multiplexed data/address bus; toggling the state of the control signal at the memory device as each data word is transferred; and suspending the transfer of the series of data words from the memory via the multiplexed data/address bus and the toggling of the state of the control signal.

FIELD OF THE INVENTION

Embodiments of this invention relate generally to an interface betweentwo integrated circuits e.g. a memory and microprocessor interface or amemory and DMA controller interface.

BACKGROUND TO THE INVENTION

One conventional microprocessor memory interface includes an addressbus, a data bus, and a control bus. The microprocessor uses the addressbus to send an memory address to the memory. The number of addresssignal lines in the address bus depends upon the number of addressablememory locations in the memory. The data bus is used to transfer datafrom the microprocessor to the memory during a write transaction and totransfer data from the memory to the microprocessor during a readtransaction. The data bus typically has 8*n data signal lines, where nis a natural number. The control bus typically includes control signallines such as write_enable (WE) that are used by the microprocessor tocontrol the type of transaction at the memory (read or write) and suchas a clock signal (clk) that is used to synchronise the transaction.

The current flash memory interface 10 used in NOKIA mobile telephones isillustrated in FIG. 1. The interface 10 has a dedicated 9-bit upperaddress bus 2 and a 16-bit multiplexed data/address bus 4. It also has acontrol bus 6 comprising: a system clock signal line (external clock) 3,a chip select signal line (CSX) 5, a read signal line (OEX) 7, anaddress valid signal line (ADVX) 9 and a Ready signal line 11.

During an initial phase of a memory access the dedicated address bus 2conveys the 9 most significant address bits while the multiplexed bus 4simultaneously conveys the 16 least significant address bits. Theaddress bits are conveyed at the rising edge of a single external clockcycle. The address valid signal line (ADVX) 9 is asserted by themicroprocessor when the multiplexed bus 4 is carrying addressinformation. This signal is typically used to latch the addressinformation from the address bus 2 and the multiplexed bus 4 into alatching device at the memory.

In a later part of the memory access, the address bus 2 is unused, whilethe multiplexed bus 4 is used to convey a data word per clock cycle.Four data words D0, D1, D2 and D3 are conveyed in series.

The interface also has a flow control mechanism that allows the memoryto pace the data transfer by temporarily suspending it. The control busincludes a Ready signal line 11 that is controlled by the memory. Thestate of the Ready signal indicates whether or not a data word is to betransferred. The Ready signal is asserted high while continuing datatransfer is possible and asserted low when continuing data transfer issuspended.

In FIG. 1 a read memory access is illustrated. The transfer of the dataword D3 from the memory to the microprocessor is delayed while the Readysignal line 11 is asserted low by the memory. The Ready signal isasserted HIGH as the fourth data word D3 is transferred from the memory.

The Ready signal line 11 enables paced burst mode access to the memoryincluding crossing internal memory page boundaries. In burst mode accessthe data is read as a burst of words, if necessary from different memorysegments used in the internal organization of the memory. The Readysignal can be used to suspend the data transfer while the next memorysegment is fetched.

It would be desirable to improve the above-described interface.

BRIEF DESCRIPTION OF THE INVENTION

According to one embodiment of the invention there is provided a methodof transferring address information from a controller device to a targetdevice via a multiplexed data/address bus comprising: transferring afirst portion of address information in a first phase via themultiplexed data/address bus; transferring a second portion of addressinformation in a second phase via a multiplexed data/address bus,wherein the first and second portions are distinct portions of theaddress information and the first and second phases are distinct andsuccessive.

According to another, embodiment of the invention there is provided acontroller device for transferring address information to a targetdevice via a multiplexed data/address bus comprising: timing means fortiming a first phase and a second phase following the first phase;addressing means for providing a first portion of address information onthe multiplexed data/address bus during the first phase and forproviding a second portion of address information on the multiplexeddata/address bus during the second phase, wherein the first and secondportions are distinct portions of the address information.

According to another embodiment of the invention there is provided atarget device for receiving address information transferred from acontroller device via a multiplexed data/address bus, the target devicecomprising: timing means for timing a first phase and a second phasefollowing the first phase; addressing means for storing, in a firstpredetermined storage location, a first portion of address informationreceived on the multiplexed data/address bus during the first phase andfor storing, in a second predetermined storage location, a secondportion of address information received on the multiplexed data/addressbus during the second phase.

According to another embodiment of the invention there is provided amethod of strobing and pacing data transfer between a controller deviceand a target device using a single control signal, comprising: strobingthe transfer of a data word from the target device to the controllerdevice by changing the state of the control signal as the data word istransferred; and pacing a transfer of data words from the target deviceto the controller device by disabling a state change of the controlsignal.

According to another embodiment of the invention there is provided atarget device for transferring data between a controller device and thetarget device, the target device comprising: an interface comprising abus for transferring data between the target device and the controllerdevice and a control signal line for providing a control signal to thecontroller; and flow control means for strobing the transfer of data tothe controller by changing the state of the control signal with eachdata word provided to the bus and for pacing the transfer of data to thecontroller by maintaining the state of the control signal.

According to another embodiment of the invention there is providedcontroller device for transferring data between a controller device andthe target device, the controller device comprising: an interfacecomprising a bus for transferring data between the target device and thecontroller device and a control signal line for receiving a controlsignal from the target device; and flow control means for latching adata word provided on the bus by the target device only when the stateof the control signal changes.

According to another embodiment of the invention there is provided amethod of strobing and pacing data transfer between a controller deviceand a target device using a single control signal, comprising: strobinga data transfer from the target device to the controller by changing thestate of the control signal with each data transfer; and pacing a datatransfer from the controller to the target by changing the state of thecontrol signal.

According to another embodiment of the invention there is provided amethod of performing a burst read access at a memory device using amultiplexed data/address bus and a control signal comprising:transferring a first portion of address information in a first phase viathe multiplexed data/address bus to the memory device; transferringsecond portion of address information in a second phase via amultiplexed data/address bus to the memory device; transferring a seriesof data words from the memory via the multiplexed data/address bus;toggling the state of the control signal at the memory device as eachdata word is transferred; and suspending the transfer of the series ofdata words from the memory via the multiplexed data/address bus and thetoggling of the state of the control signal.

Embodiments of the invention therefore provide a higher performancecontroller device/target device interface that has either a reducednumber of signal lines or has a wider data bus.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention reference will nowbe made by way of example only to the accompanying drawings in which:

FIG. 1 illustrates a prior art read memory access;

FIG. 2 illustrates a controller device and a target device connected viainterface;

FIG. 3 illustrates a 4 word burst read with pacing; and

FIG. 4 illustrates an 8 word burst write with pacing.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 2 illustrates a controller device 30 and a target device 40connected via interface 50. The controller 30 device is typically amicroprocessor, ASIC or other type of integrated circuit controller thanis able to write to and read from the target device which is typically amemory device. The interface 50 connecting the controller 30 and target40 is new. Only as many signal lines in the interface 50 will bedescribe as is necessary to understand the novel aspects of itsoperation. The interface 50 may comprise additional unspecified signallines that operate in a conventional fashion.

The interface 50 comprises: an N-bit multiplexed data/address bus 4 thatoperates a double rate, and a control bus 6 comprising a system clocksignal line (external clock) 3, a read signal line (OEX) 7, a writeenable signal line (WEX) 1, an address valid signal line (ADVX) 9 and aReady signal line 11′. The interface 50 does not comprise a dedicatedaddress bus

The interface 50 uses a new multi-phase addressing mode. Instead ofsimultaneously providing the address information via a dedicated addressbus and the multiplexed bus in a single transfer process at the risingedge of the clock cycle, the interface 50 provides the addressinformation only via a multiplexed bus 4 in a sequence of successivetransfer processes.

The address transfer may be at ‘double rate’ in which two phases ofaddress information are driven onto the multiplexed bus 4 in oneexternal clock cycle. A first address transfer phase occurs at therising edge of a first clock cycle and a second address transfer phaseoccurs at the falling edge of the first clock cycle. The first addresstransfer phase transfers N bits and the second address transfer processtransfers up to N bits. The least significant bits of the addressinformation are transferred in the first phase. This allows a singlephase short address mode to be used in which only the least significantbits of the address are transferred in the first phase and the mostsignificant bits of the address are re-used from the previous access.

The interface 50 also has a flow control mechanism that allows thetarget 40 to pace the data transfer during a write access or a readaccess by temporarily suspending the transfer. This enables paced burstmode access to the target 40, including crossing internal memory pageboundaries. In burst mode memory access the data is read/written as aburst of words, if necessary from/to different memory segments used inthe internal organization of the memory. The flow control can be used tosuspend the data transfer while the next memory segment isfetched/accessed.

The interface 50 also has a strobe mechanism that decouples the responseof the target 40, in time, from the request from the controller 30during a read access. This overcomes the problem of relative clockdelays between the controller 30 and target 40 which become morecritical as the data transfer rate is increased. This allows the newinterface 50 to operate at higher data transfer rates. The strobemechanism in the target 40 produces a strobe signal that is synchronouswith the transferred data. It is consequently received by the controller30 at the same time as the transferred data is provided on themultiplexed bus 4. The controller 30 comprises a latch mechanismoperated by the strobe signal that latches the transferred data.

Both the flow control mechanism and strobe mechanism during a read usethe Ready signal 11′ and the flow control mechanism during a write usesthe Ready signal 11′.

As in the prior art the Ready signal 11′ is controlled by the memory.However, during a read access, an absence of a state transition of theReady signal 11′ is used for data pacing (as opposed to the state of theReady signal in the prior art) and a state transition of the Readysignal 11′ is used as a strobe signal for clocking the transferred datainto the controller 30. During a write access, the state of the Readysignal 11′ is used for data pacing (as in the prior art).

The controller 30 comprises an address provider mechanism 32 and a flowcontrol slave 34. The address provider mechanism 32 receives the addressinformation 33 as an input and is connected via the interface 50 to theexternal clock signal line 3, the address valid signal line 9 and themultiplexed bus 4 as schematically illustrated in FIG. 1. The flowcontrol slave receives a control signal 35 that indicates whether theaccess using the address information should be a read access or a writeaccess. It is also connected via the interface 50 to the external clocksignal line 3, the write enable signal line WEX 1, the read enablesignal line OEX 7, the Ready signal line 11′ and the multiplexed bus 4.

The target 40 comprises an address interpreter mechanism 42, an addresslatch 44, memory circuitry 46 and a flow control master 48. The addressinterpreter mechanism 42 is connected to the external clock signal line3, the address valid signal line ADVX 9 and the multiplexed bus 4 asschematically illustrated in FIG. 1. The flow control master 48 isconnected to the external clock signal line 3, the write enable signalline WEX 1, the read enable signal line OEX 7, the Ready signal line 11′and the multiplexed bus 4. It is also connected to receive an internaldata pace signal 43 from the memory circuitry if the read or writeoperation is delayed and to transfer data to and from the memory 46 viaa data bus 41.

Burst Read Access

FIG. 3 illustrates a 4 word burst read with pacing. The Ready signal 11′is used to strobe the data into the controller 30. Each new data wordD0, D1, D2, D3 presented to the controller is accompanied by arespective change in state S0, S1, S2, S3, of the Ready signal 11′. Thedata can be paced by holding the state of the Ready signal 11 andpreventing subsequent transitions.

The read burst access begins when the address provider mechanism 32, atthe rising edge of a first clock cycle, drives and holds the addressvalid signal line ADVX LOW and simultaneously drives the N leastsignificant address bits onto the multiplexed bus 4. The addressprovider mechanism 32, at the falling edge of the same first clockcycle, then drives the remaining address bits onto the multiplexed bus 4while the address valid signal line ADVX is held LOW. The addressprovider mechanism 32, at the rising edge of the next clock cycle, thendrives and holds the address valid signal line ADVX HIGH indicating theend of the multi-phase address transfer.

The address interpreter mechanism 42 responds to a LOW address validsignal ADVX 9 and a rising edge of the external clock signal 3, bylatching the N bits received on the multiplexed bus 4 into the addresslatch 44 as the N least significant bits. The address interpretermechanism 42 responds to a LOW address valid signal and a falling edgeof the external clock signal, by latching the bits received on themultiplexed bus, if any, into the address latch 44 as the mostsignificant bits.

The flow control master 48 in the absence of a pace signal 43, latches adifferent data word D0, D1, D2 retrieved from the memory via the databus 41 onto the multiplexed bus 4 at each edge E0, E1, E2 of theexternal clock signal and simultaneously toggles the state of the Readysignal The state of the Ready signal at S0 is switched LOW as the firstdata word D0 is latched onto the multiplexed bus at the rising edge E0of the external clock signal 3. The Ready signal 11′ is the inverse ofthe external clock signal 3 with a delay.

The flow control slave 34 uses each transition S0, S1, S2 in the Readysignal 11′ to latch a different data word D0, D1, D2 from themultiplexed bus 4.

When the pace signal 43 is asserted by the memory circuitry 46, the flowcontrol master 48, continues to latch the current data word D2 on themultiplexed bus 4 and continues to hold the current state (LOW) of theReady signal 11′.

As there are no transitions in the Ready signal 11′, the flow controlslave 34 does not latch a data word from the multiplexed bus 4 and theread process is suspended.

When the pace signal 43 is de-asserted the flow control master latchesthe next data word D3 retrieved from the memory 46 via the data bus 41onto the multiplexed bus 4 at the next edge E3 of the external clocksignal 3 and simultaneously toggles the state of the Ready signal.

Flow control slave uses the transition in the Ready signal S3 to latchthe data word D3 from the multiplexed bus 4.

In the above described example, a non-return to zero Ready signal 11′ isused. The Ready signal can consequently be held in either a HIGH or LOWstate. This allows data transfers of any length to be paced at anypoint.

An alternative, although less preferred implementation, uses a return tozero Ready signal 11′ is used. The Ready signal can consequently only beheld in a LOW state. In this implementation the data must be transferredin word pairs as pacing can only occur when the Ready signal 11′ is LOW.

Burst Write Access.

FIG. 4 illustrates an 8 word burst write with pacing The state of theReady signal 11′ is used to pace data into the target 40. A LOW statewill suspend future data transfers to the target 30 and a HIGH statewill enable future data transfers to the target 30.

The write burst access begins when the address provider mechanism 32, atthe rising edge of a first clock cycle, drives and holds the addressvalid signal line ADVX LOW and simultaneously drives the N leastsignificant address bits onto the multiplexed bus of width N. Theaddress provider mechanism 32, at the falling edge of the same firstclock cycle, then drives the remaining address bits onto the multiplexedbus of width N while the address valid signal line ADVX is held LOW. Theaddress provider mechanism 32, at the rising edge of the next clockcycle, then drives and holds the address valid signal line ADVX HIGHindicating the end of the address transfer.

The address interpreter mechanism 42 responds to a LOW address validsignal ADVX 9 and a rising edge of the external clock signal 3, bylatching the N bits received on the multiplexed bus 4 into the addresslatch 44 as the N least significant bits. The address interpretermechanism 42 responds to a LOW address valid signal ADVX 9 and a fallingedge of the external clock signal 3, by latching the bits received onthe multiplexed bus 4, if any, into the address latch 44 as the mostsignificant bits.

The flow control slave 32 in the controller 30 starts the transfer ofdata by asserting WEX LOW at a rising edge of the external clock signal3 and then clocking data words D0, D1, D2, D3, D4 onto the multiplexedbus one at a time at each successive edge of the external clock signal3.

When the pace signal 43 is asserted by the memory circuitry 46, the flowcontrol master 48, stops the data transfer by de-asserting the Readysignal 11′ by making it LOW at point A in the Fig.

The flow control slave 34 responds to the LOW Ready signal 11′ bystopping the data transfer by de-asserting the write enable signal WEXat point B in the Fig. It should be appreciated that the halting of datatransfer after a change in state of the Ready signal 11′ is notinstantaneous. The halting of data transfer (point B) is delayedrelative to the change of state of the Ready signal 11′ (point A) by oneexternal clock cycle in this example.

When the pace signal is de-asserted at point C, some time later, theflow control master 48 restarts the data transfer by re-asserting theReady signal 11′ by holding it HIGH.

The flow control slave 34 responds to the HIGH Ready signal 11′ bystarting data transfer by asserting the write enable signal WEX 1 atpoint D. It should be appreciated that the re-starting of the datatransfer after a change in state of the Ready signal is notinstantaneous. The re-start of data transfer (point D) is delayedrelative to the change of state of the Ready signal 11′ (point C) by oneexternal clock cycle in this example.

Although embodiments of the present invention have been described in thepreceding paragraphs with reference to various examples, it should beappreciated that modifications to the examples given can be made withoutdeparting from the scope of the invention as claimed. For examplealthough the multi-phase transfer of the address information and thetransfer of the data between the controller and target has beendescribed using ‘double rate’ transfer, in which a transfer occurs twicewith each external clock cycle e.g. at each edge of the clock cycle,other embodiments of the invention may use ‘single rate’ transfer, inwhich a transfer occurs only once with each external clock cycle e.g.only with the rising edge of the external clock signal or,alternatively, only with the falling edge of the rising clock.

In addition, although the multi-phase transfer of an address has beenillustrated using a two-phase transfer, it should be appreciated that Nphases can be used where N is a natural number greater than 1.

Although in the interface described above the first phase, fortransferring a first portion of the address, is initiated at a firstrising clock edge and the second phase, for transferring a secondportion of the address, is initiated at a second rising clock edge, inother implementations the first phase is initiated at a first fallingclock edge and the second phase is initiated at a second falling clockedge. The first falling clock edge and second falling clock edge aresuccessive adjacent clock edges in a single clock cycle.

1. A method of strobing and pacing data transfer between a controllerdevice and a target device using a control signal, comprising: strobingthe transfer of a data word over a data bus from the target device tothe controller device by changing as the data word is transferred thestate of a signal line, in response to a state change of an externalclock, to provide the control signal wherein the signal line is distinctfrom the data bus and the external clock; and pacing an on-goingtransfer of data words from the target device to the controller deviceby disabling a state change of the signal line without disabling ongoingstate changes of the external clock, wherein disabling a state change inthe signal line can occur while the signal line is in any state.
 2. Amethod as claimed in claim 1, wherein the target device is configured tocontrol the state of the signal line.
 3. A method as claimed in claim 1,wherein the method comprises, during a burst read, strobing the transferof a series of data words from the target device to the controllerdevice by changing the state of the signal line as each data word istransferred and pacing the transfer of the series of data words from thetarget device to the controller device by disabling state change of thesignal line.
 4. A method as claimed in claim 1, wherein the methodcomprises, during a burst write, pacing the transfer of data words fromthe controller device to the target device by changing the state of thesignal line at the target device.
 5. A target device configured totransfer data between a controller device and the target device, thetarget device comprising: an interface comprising a data bus configuredto transfer data between the target device and the controller device, asignal line configured to provide a control signal to the controllerdevice and an external clock signal line, wherein the signal line isdistinct from the data bus and the external clock signal line; and astrobe mechanism configured to strobe the transfer of data to thecontroller device over the data bus by changing the state of the signalline, in response to a state change of the external clock signal line,with each data word provided to the bus and a flow control mechanismconfigured to pace an on-going transfer of data to the controller deviceby maintaining the state of the signal line without ongoing changes ofthe external clock signal line being disabled, wherein the flow controlmechanism is configured to maintain the state of the signal line in anystate.
 6. A target device as claimed in claim 5, wherein the bus is amultiplexed data/address bus.
 7. A target device as claimed in claim 5,wherein the flow control mechanism is additionally configured to pacethe transfer of data from the controller by changing the state of thesignal line.
 8. A target device as claimed in claim 5, configured tooperate as a memory device.
 9. A target device as claimed in claim 5,wherein pacing an on-going transfer of data words from the target deviceto the controller device is achieved by disabling a state change of thesignal line.
 10. A controller device configured to transfer data betweenthe controller device and a target device, the controller devicecomprising: an interface comprising a data bus configured to transferdata between the target device and the controller device, a signal lineconfigured to receive a control signal from the target device and anexternal clock signal line, wherein the signal line is distinct from thedata bus and the external clock signal line; and a flow controlmechanism configured to latch a data word provided on the bus by thetarget device during an on-going transfer of data words only when thestate of the signal line changes, wherein the state of the signal linechanges in response to a state change of the external clock signal line,and wherein the flow control mechanism is configured not to latch a dataword if the state of the signal line is maintained in any state withoutongoing state changes of the external clock signal line being disabled.11. A controller device as claimed in claim 10, wherein the bus is amultiplexed data/address bus.
 12. A controller device as claimed inclaim 10, wherein the flow control mechanism is configured to suspendthe transfer of data to the target device via the bus when the state ofthe signal line changes.
 13. A method of strobing and pacing datatransfer between a controller device and a target device using a controlsignal, comprising: strobing a data transfer from the target device tothe controller device over a data bus by toggling only with each datatransfer the state of a signal line, in response to a state change of anexternal clock, to provide the control signal wherein a data word is nottransferred if the state of the signal line is maintained in any stateand without disabling ongoing state changes of the external clock andwherein the signal line is distinct from the data bus and the externalclock; and pacing an on-going data transfer from the controller deviceto the target device by changing the state of the signal line.
 14. Amethod of performing a burst read access at a memory device using amultiplexed data/address bus and a control signal comprising:transferring a first portion of address information in a first phase viathe multiplexed data/address bus to the memory device; transferring asecond portion of address information in a second phase via themultiplexed data/address bus to the memory device; transferring a seriesof data words from the memory device via the multiplexed data/addressbus; toggling only as each data word is transferred the state of asignal line, in response to a state change of an external clock, toprovide the control signal at the memory device wherein the signal lineis distinct from the data bus and the external clock; and suspending anon-going transfer of the series of data words from the memory device viathe multiplexed data/address bus and suspending the toggling of thestate of the signal line without disabling ongoing state changes of theexternal clock, by maintaining the signal line in any state.